1. Field of the Invention
The present invention relates to a process and apparatus for reclaiming organic contaminants from gases. More particularly, the process is adapted to economically recover valuable organic materials from contaminated air and to return purified air to the environment or to a process area.
2. Description of the Prior Art
Heretofore, processes for the recovery and/or safe disposal of organic contaminants in gases were known.
Organic contaminants have been deposited on adsorbent materials which have been stripped or regenerated by steam. It is known that the process of steam regeneration is not efficient for low concentrations of organic contaminants nor is the process energy efficient.
Organic contaminants have been deposited on adsorbent materials which have been stripped or regenerated in a partial vacuum. A partial vacuum enhances the evaporation effect and the stripping action. It is known that this vacuum process is limited to fixed bed adsorbers which require cyclical operation. A vacuum alone is insufficient to strip or remove high boiling point contaminants. Further, it is known that the evaporation effect absorbs heat, accordingly, additional energy is required for heating gases in a vacuum regeneration process.
Hot gases have been employed to strip contaminants from adsorbent materials. In my U.S. Pat. No. 3,455,089 there is shown a process for periodically regenerating contaminant bearing adsorbent materials. A feature of this patent teaches that the stripped contaminants may be incinerated to produce the energy to heat the hot regenerating gases by directly mixing or indirectly heat exchanging. It is known that direct mixing of the incinerated contaminants may provide a partially inert regenerating gas.
In my U.S. Pat. No. 3,534,529 there is shown a cascade process for periodically regenerating contaminant bearing adsorbent materials with hot gases. A feature of this patent teaches that the stripped contaminants may be removed and recovered in a secondary adsorber and then stripped with steam which can be condensed to provide a mixture of water and the stripped contaminants. This recovery system requires decanting of the recovered liquid mixture or fractionation as the case may be.
While the teachings of U.S. Pat. Nos. 3,455,089 and 3,534,529 suggest that the incineration of the contaminants would leave nothing for recovery, any attempt to achieve a partial incineration of the contaminants would be self-defeating. There would be an incomplete combustion of the contaminants which would result in destruction of the formerly recoverable contaminants and also atmospheric pollution of the exhaust.
If a compromise is attempted and a portion of the recoverable contaminants is incinerated the major portion of the capital equipment of both aforementioned patents is still required.
It is conservatively estimated that a large automotive assembly plant which exhausts one million cubic feet of air per minute from its solvent contaminated assembly and painting areas discharges in excess of 8,000 gallons of solvent per eight hour shift. It would require 11,400 cubic feet of natural gas per minute to incinerate this solvent in the contaminated air even if you allow for a sixty percent recovery of the heat from the incinerator.
Heretofore, it was not economically feasible to justify the capital equipment cost of a contaminant recover system due to the high capital cost and low efficiency of the system.
The present invention, organic contaminant recovery system, is capable of paying for its capital cost in less than ten years based on the recovery of 4,000 gallons per day or fifty percent of the usual paint solvent employed by automotive assembly plants.
It would be desirable to be able to recover a complete range of low to high boiling point organic contaminants from gases in either a low or high concentration using the same process and apparatus. Further, it would be desirable to provide an apparatus and system which is more efficient than prior art processes and is cheaper than apparatus known in the prior art.